I would add to the first answer that another reason for the conflict is Mrs. Merriweather's reference to Atticus helping Tom Robinson; it is clear that she does not approve of it. After she complains to the other women that "some people" think they're doing the right thing by defending Tom, Miss Maudie snaps, and I paraphrase here: "His food doesn't stick going down, does it?"

This is Maudie's way of showing her disapproval of Mrs. Merriweather's absurd, racist remarks, and especially her attempt to criticize Atticus (while eating his food!)

This is after Tom Robinson's trial has finished. Miss Maudie and Mrs. Merriweather and some other ladies are at the Finches' home for the Missionary Circle meeting. This is where the conflict comes in.

Miss Merriweather and the others are saying horrible things about black people in general and about specific black people as well. Miss Merriweather in particular is complaining about her cook and how she is moping around because of the Robinson verdict. Miss Maudie thinks that she is complaining to much and that she should have more understanding. This is why she kind of snaps at Mrs. Merriweather.